US2825864A

US2825864A - Nonlinear resistance bridge utilizing transformer providing time delay compensation

Info

Publication number: US2825864A
Application number: US446592A
Authority: US
Inventors: William F Eagan
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1954-07-29
Filing date: 1954-07-29
Publication date: 1958-03-04
Anticipated expiration: 1975-03-04

Description

March 4, 1958 2,825,864 NONLINEAR RESISTANCE BRIDGE UTILIZING TRANSFORME Filed July 29, 1954 W F EAGAN R PROVIDING TIME DELAY COMPENSATION 2 Sheets-Sheet 1 C 67 g! A c 11121:

4 T T W 1? mwz/wbo/i.

gang ow.

March 4, 1958 w. F. EAGAN 2,825,864

NONLINEAR RESISTANCE BRIDGE UTILIZING TRANSFORMER PROVIDING TIME DELAY COMPENSATION 2 Sheets-$heet 2 Filed July 29, 1954 NONLlNEAR RESHSTANQE BRIDGE UTILIZING TRANSFORMER PRGVIDl-[NG TIME DELAY COMPENSATION William F. Eagan, West Allis, Wis,

assignor to Allis- Chalmers Manufacturing Company,

This invention relates in general to voltage error detecto'rs and in particular to time delay compensating means for detectors utilizing linear and nonlinear resistors.

Voltage error detector bridge circuits utilizing linear and nonlinear resistors are known in which the inherent time delay of the nonlinear resistors is compensated for by capacitors connected across some of the branches of the bridge circuit.

A disadvantage of these known circuits is that they cannot readily be used in aircraft at high altitudes where low temperatures exist. This is because electrolytic capacitors are not reliable at low temperatures and oil filled capacitors are too heavy and occupy too much volume. Neither type of capacitor is therefore suited for use in a bridge circuit installed in an aircraft.

The invention overcomes this disadvantage by providing, in a linear-nonlinear resistor bridge circuit, a transformer having one winding connected across the input junctions of the bridge and another winding connected in series with the output junctions of the bridge. The transformer affords reliable time delay compensation at extremely low temperatures and is relatively small and light in weight.

It is therefore an object of this invention to provide a voltage error detector of the linear-nonlinear resistor type having time delay compensating means reliable at low temperatures and relatively light in weight and small in volume.

Other objects and advantages will appear from the following detailed description when read in connection with the accompanying drawings, in which:

Fig. 1 diagrammatically illustrates one embodiment of the invention as applied to a rectifying system;

Fig. 2 shows in more detail, a saturable reactor shown in Fig. 1;

Fig. 3 is a graph illustrating the transfer characteristic'of the reactor shown in Fig. 2;

Fig. 4 shows, in more detail, a saturable reactor shown in Fig. 1;

Fig. 5 is a graph illustrating the transfer characteristic of the reactor shown in Fig. 4;

Fig. 6 shows, in more detail, a saturable reactor shown in Fig. 1;

Fig. 7 a is graph illustrating the transfer characteristic of the reactor shown in Fig. 6; and

Fig. 8 is a graph illustrating the transfer characteristic of a bridge circuit shown in Fig. 1.

In the drawing, where an underlined reference numeral appears in proximity with a plurality of lower case reference letters, the numeral indicates a means comprising a plurality of elements and the elements are indicated by the lower case reference letters. In the specification, these elements are identified by the reference numeral accompanied by the reference letter.

Referring to Fig. l, the invention is shown embodied in a rectifying system wherein a main rectifier 20 sup- Patent 0 plies direct current to a load device 11. The direct current terminals of the rectifier 20 are connected to output terminals 12, 13 through a well known filtering arrangement comprising capacitor 14 and choke coils i6, 17 to impress a direct current voltage across output terminals 12, 13 for providing a direct current voltage source for load device 11 which is connected across terminals 12, 13 by means of cables or conductors i3, 19. The alternating current terminals of the rectifier 20 are connected through a transformer 22 and the reactanc'e' windings of a s'a'turable reactor 21 to an alternating current source of substantially constant voltage such as an alternating current" generator 23.

Saturable reactor 21 has a core 21a, a pair of reactance windings 21b, a pair of rectifiers 210, a bias winting 21d and a signal winding 21c. Rectifiers 21c provide self-saturation or self-excitation for the reactor The bias winding 21d and signal winding 1212 act in opposition to each other to determine the reactance of reactance windings 21b to control the voltage applied to transformer 22 and rectifier 20 and thus to control the direct current voltage of rectifier 20 impressed across output terminals 12, 13. Bias winding 21d of reactor 21 is connected to the direct current terminals of rectifying device 24 through an adjustable resistor 26. The alternating current terminals of rectifying device 24' are connected to a transformer 27 which is energized by alte'rnating current generator 23. The bias winding 21d thus has impressed thereon a substantially constant unidirectional bias voltage, the value of which is determined by the setting of resistor 26. Signal winding He is connected through an adjustable resistor 28 to the di rect current terminals of a second rectifier 30. The direct current voltage output of rectifier 30 is controlled by a saturable reactor 31.

Reactor 31 has a core 31a, a pair of reactance windings 31b, a pair of rectifiers 310, a current limit control winding 31, a voltage control winding 31c and a feedback winding 31). Reactance windings 31b and rectifiers 310 are serially connected with the alternating current terminals of rectifier 30 to transformer 27. Signal winding 21s of reactor 21 thus has impressed-thereon a unidirectional signal voltage, the magnitude of which depends upon the net effect of windings 31d, 31e of reactor 31.

Reactors

21 and 31 are included in the voltage regulator portion of the system. Winding 31s is the voltage responsive element and winding 31d is the current limit responsive element of the voltage regulator.

The direct current output voltage of rectifier 30 is fed back into feedback winding 31f through a capacitor 32 and an adjustable resistor 33 to prevent the system from overshooting and oscillating during the voltage recovery. The setting of resistor 33 determines the speed and manner of recovery.

Voltage control winding 31c is connected to respond to the output of a voltage error detector comprising a bridge circuit 34 and a transformer 36. The bridge circuit 34 comprises four resistors, at least one of which is a nonlinear voltage dependent resistor. As shown, the bridge circuit 34 has a pair of nonlinear voltagedependent resistors such as tungsten filament light bulbs 34a connected in series with a pair of linear or constant adjustable resistors 34b to form a bridge circuit 34. A first pair of opposite junctions 340 of the bridge circuit are connected across output terminals 12, 13 of the rectifying system to have the direct current voltage of rectifier 20 impressed on junctions 34c. The constant-r sistors 34b may be adjusted to cause the voltage across the other pair of opposite junctions 34a. to be approximately zero for the desired value of the controlled volt;-

age across terminals 12, 13 and to vary in magnitude and direction with variations in the controlled voltage from the desired value.

A rheostat 35 may be used to caused the bridge circuit 34 to balance at any desired value of the controlled voltage which is impressed across junctions 340. A reduction of the resistance of rheostat 35 causes the bridge circuit to balance at a lower value of the controlled voltage.

Transformer 36 has a first winding 36a connected in series with an adjustable resistor 37 across input junctions 34c, and a second winding 36b connected in series with output junctions 34a, an adjustable resistor 38 and voltage control winding 31:; of saturable reactor 31. Voltage control winding 31e thus has impressed thereon a direct current reversible polarity control voltage which varies in direction and magnitude with variations in the controlled direct current voltage of rectifier 20 appearing across output terminals 12, 13.

The time delay inherent in the nonlinear voltage dependent resistors 34a is compensated for by transformer 36. Any change in the input to the bridge circuit at junctions 34c is sensed by transformer winding 36a and is immediately reflected into transformer Winding 36b which is in series with junctions 34d and voltage control winding 31c. Voltage control winding 31:: thus senses the change without time delay. Resistor 37 is adjusted to obtain the desired speed of response. The disadvantage of the inherent time delay in the nonlinear resistors is thus overcome.

The voltage impressed on current limit control Winding 31d of reactor 31 is controlled by a current limit device comprising a saturable reactor 41 and a bridge circuit 47. Winding 31d is connected through an adjustable resistor 39 to the direct current terminals of a rectifier 40. The direct current output voltage of rectifier 40 is controlled by saturable reactor 41.

Reactor 41 has a core 41a, a pair of reactance windings 41b, a pair of rectifiers 410, a saturating winding 41d and a damping winding 41c. Reactance windings 41b and rectifiers 410 are serially connected with the alternating current terminals of rectifier 40 to transformer 27. There is thus impressed on current limit control winding 31d of reactor 31 a unidirectional current limit control voltage, the magnitude of which depends upon the net efiect of saturating winding 41d and damping winding 412.

Damping winding 41e is connected through an adjustable resistor 42 to the output winding 43a of a damping transformer 43. An input winding 43c of this damping transformer is connected through an adjustable resistor 44 to the direct current output terminals of rectifier 30. The conductor carrying the direct current output of main rectifier 20 acts as another input winding 43b for damping transformer 43. Transformer 43 thus senses changes in the direct current in the load device 11 and changes in the output of rectifier 30 to impress a damping signal across damping winding 412. A rectifier 46 is connected across winding 41e to cause it to receive damping signals of one direction only.

Saturating winding 41d is connected to respond to the output of a bridge circuit 47. The bridge circuit 47 comprises four resistors, at least one of which is a nonlinear resistor. As shown, the bridge circuit 47 has a pair of nonlinear resistors such as tungsten filament light bulbs 47a and a pair of linear or constant adjustable resistors 47b connected therewith in series to form a bridge circuit having a pair of opposite input junctions 47c and a pair of opposite output junctions 47d.

Rectifier 48 has its direct current terminals connected through resistor 38 to input junctions 47c. The alternating circuit terminals of rectifier 48 are fed from a current transformer 50 in the alternating current line that feeds main rectifier 20. Input junctions 47c thus have impressed thereacross from rectifier 48, a unidirectional voltage dependent upon the direct current in load device 11.

Input junctions 570 also are connected to the direct current terminals of rectifier 3-9. The alternating current terminals of rectifier 49 are connected to transformer 27. Input junctions 47c therefore also have impressed thereacross, from rectifier a substantially constant unidirectional reference voltage.

The output junctions .74! of the bridge circuit are connected to saturating winding 41d of reactor all to impress thereon a reversible unidirectional voltage dependent upon the value of the direct current in load device 11.

Fig. 2 shows in detail the connections for the main saturable reactor 21. Bias winding 21d is wound and energized so that its ampere turns oppose the ampere turns due to the direct current component in reactance windings 21b and rectifiers 21c. Signal Winding 212 is Wound and energized so that its ampere turns aid the ampere turns due to the direct current component of the current in reactance windings 21b and rectifiers Zlc. Increases in current through signal windings 21e cause increases in the direct current voltage of the main rectifier 2t) and decreases of said current cause decreases of said voltage.

Fig. 3 is a graph showing the transfer characteristic 51 of saturable reactor 21. The abscissa represents the net ampere turns of windings 21d, 212 and the ordinate represents the direct current voltage of main rectifier 20.

Fig. 4 shows in detail the connections for saturable reactor 31. Current limit control winding 31d is wound and energized so that its ampere turns oppose the ampere turns due to the direct current component of the current in reactance windings 311: due to rectifiers 31c. Voltage control winding 31a may either aid or oppose the saturation of the reactor in response to the reversible unidirectional output voltage of bridge circuit 34 which is impressed on Winding 312. When the direct current voltage of main rectifier 24B is below the desired value, the ampere turns of winding 31:: act to increase the voltage impressed on signal winding Zle of reactor 21. When the direct current voltage of main rectifier 20 is above the desired value, the ampere turns of winding 31a act to decrease the voltage impressed on signal winding 21c of reactor 21.

Fig. 5 is a graph showing the transfer characteristic curve 52 of saturable reactor 31. The abscissa represents the net ampere turns of windings 31d, 31e and the ordinate represents the signal voltage impressed on winding 21a of reactor 21.

Fig. 6 shows the details of the connections for saturable reactor 41. Saturating winding 41d has impressed thereon a reversible unidirectional voltage and therefore its ampere turns may either aid or oppose the ampere turns due to the direct current component in reactance windings 41b due to rectifiers 41c and therefore may either increase or decrease the unidirectional voltage impressed on current limit control winding 31d of reactor 31. Damping winding 41c, because of rectifier 46 connected thereacross has an appreciable effect only upon a decrease in the current load device 11, whereupon its ampere turns act to decrease the voltage of current limit control winding 31d of reactor 31.

Fig. 7 is a graph showing the transfer characteristic curve 53 of saturable reactor 41. The abscissa represents the ampere turns of saturating Winding 41d and the ordinate represents the voltage impressed on current limit control winding 31d of reactor 31.

Fig. 8 is a graph showing the transfer characteristic curve 54 of the current limit bridge circuit 47. The abscissa represents the voltage across input junctions 470 which is dependent upon the load current and the ordinate represents the voltage across output junctions 4711 which is impressed on saturating winding 41d of reactor 41. The reference voltage impressed on input juncass-ease tions 47c by rectifier 49 is represented by 56. This reference voltage causes a voltage output represented by 57 and prevents operation on the dash line portion of the curve. As long as the voltage of rectifier 48 is equal to or less than that of rectifier 49, the bridge circuit operates at a point 76 on the curve. When the voltage of rectifier 48 exceeds the reference voltage of rectifier 49, the bridge circuit may operate at any point on the curve to the right of point 7d and the bridge output at output junctions 47d varies in dependence upon the voltage of rectifier 43. For a voltage of rectifier as represented by 58, which is the voltage corresponding to the limit value of the load current, the bridge operates at point 80 to have an output voltage represented by 59. For voltages of rectifier 48 higher than voltage 58, the bridge output decreases to become zero at point 9%; and then reverses in direction and increases in magnitude for still further increases in the voltage of rectifier 43.

Points

71, 81 and 91 on the curve 53 in Fig. 7 corresponds to points 70, Si) and 90 on curve 54 in Fig. 8.

in the operation of the system, the direct current voltage of main rectifier impressed across terminals 12, 1.3, is controlled according to so-called knee curve regulation to maintain the voltage across load device 11 substantially constant as load current therethrough varies from zero up to a predetermined limit value.

The load device could be, for example, an airplane starting motor having a low thermal capacity. The load current must therefore be carefully controlled so as not to overheat the motor during the starting period. When such a motor is thrown on the system, its current would be limited only by the total resistance of its armature circuit unless its terminal voltage is reduced. As

the motor accelerates and develops a counter electromotive force, the voltage can be increased and the current still held under the predetermined limit value. The voltage will keep increasing until the knee of the voltage current curve is reached, at which point the load current drops off and the motor runs on almost constant voltage.

The direct current output voltage of the main rectifier 20 is controlled in the following manner.

Assume that the voltage across terminals 12, 13 falls below its predetermined desired value. The bridge circuit 34 unbalances and an output voltage appears across output junctions 34d causing a control voltage to be impressed on voltage control winding 31s of reactor 31. This control voltage is in the direction to increase the voltage impressed on signal winding lie of reactor 21 to thus increase the direct current voltage of the main rectifier 20 until the predetermined desired value is reached to thus bring the bridge circuit 34 back toward balance. When the direct current voltage of main rectifier Zfi rises above its predetermined desired value, the operation is the reverse of that just described.

Line drop compensation for the voltage drop in lines 13, 19 must be provided to maintain the voltage across load device 11 constant in the face of varying current in the load device. Line drop compensation is provided by the current limit device comprising bridge circuit 47 and saturable reactor 41 when the load current is above a predetermined normal value such as the value corresponding to point '70 in Fig. 8 and below a predermined limit value such as the value corresponding to point 80 in Fig. 8. The transfer characteristic curve 53 of reactor 41, shown in Fig. 7, is such that between

points

71 and 81, as the load current in load device 11 increases, the current limit control voltage impressed on current limit control winding 31d decreases, thus allowing the signal voltage impressed on signal winding 21a to increase to thus increase the direct current voltage of the main rectifier 29. Line drop compensation is thus accomplished to enable the voltage regulator to maintain the voltage of the load device constant in the face of increasing load current between a predetermined normal value and a predetermined, limit value.

Below the normal value of current, the current limit device maintains a constant output to prevent the occurrence of the reverse of line drop compensation which would occur if the bridge circuit 47 did not have a refence voltage impressed thereon by rectifier 49. Without the reference voltage, the signal voltage impressed on signal winding 21c would increase in response to increases of the load current between zero and the predetermined normal value to accomplish the undesirable reverse of line drop compensation and would thereby hinder the voltage regulator tending to prevent it from maintaining the load voltage constant.

When the load current reaches its limit value, rectifier 48 produces a voltage indicated at 58 which causes bridge circuit 47 to operate at point and saturable reactor 41 to operate at point 81. If the load current exceeds this limit value the output of reactor 41 increases greatly, causing the voltage impressed on current-limit control winding 31d to increase greatly. This greatly decreases the voltage of signal winding 21a to greatly decrease the direct current voltage of the main rectifier 20 thereby limiting the load current to the predetermined desired value.

The current limit device thus provides both current limit action and line drop compensation. The line drop compensation is efiective for load currents in a range between a predetermined normal value and a predetermined limit value. This is the range where line drop compensation is most needed because the current values are high. The line drop compensation action stops and the current limiting action begins when the current exceeds the limit value.

Additional line drop compensation may be obtained by modulating the voltage output across junctions 34d by the voltage drop in resistor 38. Resistor 38 is connected through rectifier 48 to current transformer 50 and is thus traversed with a current proportional to the load current in load device 11. This modulation compensates for the voltage drop in

cables

18, 19 to enable the voltage regulator to maintain the voltage of the load substantially constant over the entire range of varying load current regardless of the voltage drop in the cables.

Features disclosed but not claimed herein are claimed in application of William F. Eagan and Roger L. Robertson, Serial No. 446,593, filed July 29, 1954, now issued Patent U. S. 2,723,372. I

Although only one embodiment of the invention has been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications -50 may be made therein without departing from the spirit of the invention and the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, one of said resistors being a nonlinear voltage dependent resistor, means connecting one pair of said opposite junctions to a variable voltage source, means connecting the other pair of said opposite junctions to a voltage responsive element for impressing on said element a voltage varying in magnitude with variations of the voltage of said source from a predetermined value, and time delay compensation means comprising a transformer having a first winding connected across said one pair of opposite junctions and a second winding connected in series with said element.

2. A voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, one of said resistors being a nonlinear voltage dependent resistor, means connecting one pair of said opposite junctions to a variable unidirectional voltage source, means connecting the other pair of said opposite junctions to a voltage responsive element for impressing on said element a reversible unidirectional voltage varying in direction and magnitude with variations of the voltage of said source from a predetermined value, and time delay compensation means comprising a transformer having a first winding connected across said one pair oftopposite junctions and a second winding connected in series with said element.

3-. In combination, a first rectifier, a source of alternating current for energizing said first rectifier, a first saturable reactor having a first reactance winding in series with said source and having a bias winding and a signal winding acting in opposition for controlling the direct current voltage of said first rectifier, means for impressing a substantially constant unidirectional voltage on said bias winding, a second saturable reactor having a second reactance winding, means including a second rectifier connecting said source to said second reactance winding in series with said signal winding for impressing a unidirectional signal voltage on said signal winding, said second saturable reactor having a voltage control winding for controlling the magnitude of said signal voltage, and a voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, one of said resistors being a nonlinear voltage dependent resistor, means connecting one pair of said opposite junctions to be energized by the direct current voltage of said first rectifier, means connecting the other pair of said opposite junctions to said voltage control winding for impressing thereon a reversible unidirectional voltage varying in direction and magnitude with variations of said direct current voltage of said first rectifier from a predetermined value to vary the impedance of said reactance windings for maintaining the direct current voltage of said first rectifier substantially constant at said predetermined value, and time delay compensation means comprising a transformer having a first winding connected across said one pair of opposite junctions and a second winding connected in series with said voltage control winding.

4. A voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, two of said resistors being nonlinear voltage dependent resistors, said nonlinear re sistors being disposed in opposite arms of said bridge circuit, means connecting one pair of said opposite junctions to a variable voltage source, means connecting the other pair of said opposite junctions to a voltage responsive element for impressing on said element a voltage varying in magnitude with variations of the voltage of said source from a predetermined value, and time delay compensation means comprisinga transformer having a first winding connected across said one pair of opposite junctions and a second winding connected in series with said element.

5.-A voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, two of said resistors being nonlinear voltage dependent resistors, said nonlinear resistors being disposed in opposite arms of said bridge circuit, means connecting one pair of said opposite junctions to a variable unidirectional voltage source, means connecting the other pair of said opposite junctions to a voltage responsive element for impressing on said element a reversible unidirectional voltage varying in direction and magnitude with variations of the voltage of said source from a predetermined value, and time delay compensation means comprising a transformer having a first winding connected across said one pair of opposite junctions and a second winding connected in series with said element.

6. In combination, a first rectifier, a source of alternating current for energizing said first rectifier, a first saturable reactor having a reactance winding in series with said source and having a bias winding and a signal winding acting in opposition for controlling the direct current voltage of said first rectifier, means for impressing a substantially constant unidirectional voltage on said bias winding, a second saturable reactor having a second reactance winding, means including a second rectifier connecting said source to said second reactance winding in series with said signal winding for impressing a unidirectional signal voltage on said signal winding, said second saturable reactor having a voltage control winding for controlling the magnitude or" said signal voltage, and a voltage error detector comprising four resistors connected in series to form a bridge circuit having two pairs of opposite junctions, two of said resistors being nonlinear voltage dependent resistors, said nonlinear resistors being disposed in opposite arms of said bridge circuit, means connecting one pair of said opposite junctions to be energized by the direct current voltage of said first rectifier, means connecting the other pair of said opposite junctions to said voltage control winding for impressing thereon a reversible unidirectional voltage varying in direction and magnitude with variations of said direct current voltage of said first rectifier from a predetermined value to vary the impedance of said reactance windings for maintaining the direct current voltage of said first rectifier substantially constant at said predetermined value, and time delay compensation means comprising a transformer having a first winding connected across said one pair of opposite junctions and a second winding connected in series with said voltage control winding.

N 0 references cited.